The present invention relates to an apparatus for removing a coated film from a peripheral portion of a substrate, particularly a substrate for a liquid crystal display (LCD) device.
In general, a photolithography technology is employed in the manufacture of an LCD device for forming an electrode pattern of an indium tin oxide (ITO) thin film on a glass substrate. In the photo-lithography technology, a photoresist solution is dripped onto an LCD substrate which is kept rotated by a spin chuck so as to form a photoresist film of a uniform thickness over the entire surface of the substrate, followed by exposing the photoresist film to light in a predetermined pattern and subsequently developing the patterned film.
If the LCD substrate the rotation of which is stopped after formation of the photoresist film is. left to stand, the resist film in a peripheral portion of the substrate is rendered thicker than that in a central portion of the substrate. The non-uniformity of the film thickness is considered to be caused by a surface tension acting on the soft resist film containing a solvent. It should also be noted that, in the coating step, the resist solution flows into a peripheral portion on a back surface of the substrate, with the result that resist which is not required for forming a circuit pattern is attached to the substrate. It is impossible to eliminate completely the non-uniformity of the resist film thickness or to remove completely the undesired resist coating from the peripheral portion of the substrate in the developing step. Therefore, the resist partly remains in the peripheral portion of the substrate after the developing step. When the remaining resist is dried, the dry resist peels off the substrate so as to generate particles.
A measure for avoiding the particle generation is proposed in, for example, Japanese Patent Disclosure (Kokai) No. 8-131971. Disclosed in this prior art is an apparatus for removing the resist coating from a peripheral portion of a substrate immediately after the resist coating step. The apparatus comprises a solvent discharge section having a length substantially equal to one side of an LCD substrate and positioned to face the substrate such that a solvent is discharged to cover the entire peripheral portion on one side of the substrate. While the solvent discharge section, from which a solvent is being discharged toward the substrate, is horizontally moved along the substrate from an inner region toward an outer region of the substrate, the dissolved resist is removed by suction through a suction discharge passageway. It is also taught that the dissolved resist is removed by suction through a suction discharge passageway while the solvent discharge section, through which a solvent is being discharged, is gradually inclined toward a peripheral portion of the substrate.
In this prior art, however, the dissolved resist tends to be deposited and accumulated in the vicinity of a peripheral edge of the substrate so as to remain there. This tendency is strong particularly in a large LCD substrate, making it impossible to remove completely the resist coating from the peripheral edge of the substrate. It should be noted that, in the case of using a solvent discharge section large enough to cover entirely one side of the LCD substrate, it is impossible to remove completely the materials dissolved in the solvent from the LCD substrate unless the apparatus is equipped with a suction discharge mechanism of a markedly large capacity. However, if the apparatus is equipped with a large pump having a large suction discharge capacity in order to remove completely the dissolved resist, both the facility cost and the running cost are prominently increased.